Lens structure configured to increase quantum efficiency of image sensor

ABSTRACT

Various embodiments of the present disclosure are directed towards an image sensor having a substrate including a plurality of sidewalls that define a plurality of protrusions along a first side of the substrate. The substrate has a first index of refraction. A photodetector is disposed within the substrate and underlying the plurality of protrusions. A plurality of micro-lenses overlying the first side of the substrate. The micro-lenses have a second index of refraction that is less than the first index of refraction. The micro-lenses are respectively disposed laterally between and directly contact an adjacent pair of protrusions in the plurality of protrusions. Further, the micro-lenses respectively comprise a convex upper surface.

REFERENCE TO RELATED APPLICATION

This Application claims the benefit of U.S. Provisional Applicationnumber 62/928,559, filed on Oct. 31, 2019, the contents of which arehereby incorporated by reference in their entirety.

BACKGROUND

Many modern day electronic devices (e.g., digital cameras, opticalimaging devices, etc.) comprise image sensors. Image sensors convertoptical images to digital data that may be represented as digitalimages. An image sensor includes an array of pixel sensors, which areunit devices for the conversion of an optical image into digital data.Some types of pixel sensors include charge-coupled device (CCD) imagesensors and complementary metal-oxide-semiconductor (CMOS) image sensors(CIS). Compared to CCD pixel sensors, CIS are favored due to low powerconsumption, small size, fast data processing, a direct output of data,and low manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of animage sensor including a substrate with a plurality of protrusions, anda plurality of micro-lenses disposed over and spaced laterally betweenthe protrusions.

FIG. 2 illustrates a cross-sectional view of some alternativeembodiments of the image sensor of FIG. 1, in which a plurality ofsemiconductor devices are disposed on a front-side surface of thesubstrate.

FIGS. 3A-B illustrate cross-sectional views of some alternativeembodiments of the image sensor of FIG. 2, in which light filtersoverlie the plurality of micro-lenses.

FIGS. 4-9 illustrate cross-sectional views of some embodiments of amethod of forming an image sensor that includes a substrate with aplurality of protrusions, and a plurality of micro-lenses disposed overand spaced laterally between the protrusions.

FIG. 10 illustrates a method in flow chart format that illustrates someembodiments of forming an image sensor that includes a substrate with aplurality of protrusions, and a plurality of micro-lenses disposed overand spaced laterally between the protrusions.

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples,for implementing different features of this disclosure. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

CMOS image sensors (CIS) typically comprise an array of pixel regions,which respectively have a photodetector arranged within a semiconductorsubstrate. Light filters (e.g., color filters, infrared (IR) filters,etc.) are arranged over the photodetectors and are configured to filterincident light provided to different photodetectors within the CIS. Uponreceiving light, the photodetectors are configured to generate electricsignals corresponding to the received light. The electric signals fromthe photodetectors can be processed by a signal processing unit todetermine an image captured by the CIS. Quantum efficiency (QE) is aratio of the numbers of photons that contribute to an electric signalgenerated by a photodetector within a pixel region to the number ofphotons incident on the pixel region. It has been appreciated that theQE of a CIS can be improved with on-chip absorption enhancementstructures.

An absorption enhancement structure may include a plurality ofprotrusions arranged along a surface of the semiconductor substrate. Theabsorption enhancement structure can increase absorption by decreasingthe reflection of incident radiation. Further, a passivation layeroverlies the absorption enhancement structure and fills recesses betweenthe plurality of protrusions. During formation of the passivation layerover the absorption enhancement structure, an anti-reflective coating(ARC) layer is formed over the passivation layer. Subsequently, the ARClayer and the passivation layer are etched at a same rate until a topsurface of the protrusions is reached, such that the passivation layerhas a substantially flat top surface. However, as incident radiationpasses through the substantially flat top surface of the passivationlayer to the plurality of protrusions, it may be reflected off asidewall of a protrusion away from an underlying photodetector. This maybe because the incident light travels along a path that is approximatelyperpendicular to the substantially flat top surface of the passivationlayer and may not be focused towards the underlying photodetector. Thereflected radiation may be directed towards an adjacent underlyingphotodetector, thereby causing cross-talk between photodetectors and/orreflected away from the pixel region. Further, the reflected radiationmay be directed away from the semiconductor substrate, therebydecreasing incident radiation disposed upon the underlyingphotodetector. This in part may decreasing a QE of the underlyingphotodetector.

Accordingly, some embodiments of the present disclosure are directedtowards an image sensor including a substrate with a plurality ofprotrusions, and a plurality of micro-lenses, each having a convex uppersurface, overlying and spaced laterally between the protrusions. Forexample, during fabrication of the image sensor, a photodetector isformed in a substrate and a plurality of protrusions is formed along aback-side surface of the substrate. A passivation layer is formed overthe plurality of protrusions, such that the passivation layer fills aplurality of recesses disposed between the plurality of protrusions. AnARC layer is formed over the passivation layer and a partial etch isperformed on the ARC layer until an upper surface of the passivationlayer is reached, thereby leaving at least a portion of the ARC layerover the passivation layer. Further, one or more high selectivity etchprocesses are performed on the ARC layer and passivation layer, suchthat the passivation layer is etched at a higher rate than the ARClayer. This, in part, defines a plurality of micro-lenses over theplurality of protrusions, such that a micro-lens is disposed betweeneach adjacent pair of protrusions and each micro-lens has a convex uppersurface. By virtue of the convex upper surface, the micro-lenses areconfigured to focus incident radiation towards a focus point betweeneach adjacent pair of protrusions, thereby decreasing reflection ofincident radiation and increasing incident radiation directed towardsthe photodetector. This, in turn, increases a QE of the image sensor.

FIG. 1 illustrates a cross-sectional view of some embodiments of animage sensor 100 including a substrate 104 with a plurality ofprotrusions 110, and a plurality of micro-lenses 112 disposed over andspaced laterally between the protrusions 110.

The image sensor 100 includes an interconnect structure 102 disposedalong a front-side 104 f of the substrate 104. In some embodiments, thesubstrate 104 comprises any semiconductor body (e.g., bulk silicon,epitaxial silicon, another suitable semiconductor material, or the like)and/or has a first doping type (e.g., p-type doping). A photodetector108 is disposed within the substrate 104 and is configured to convertincident electromagnetic radiation 114 (e.g., photons) into electricalsignals (i.e., to generate electron-hole pairs from the incidentelectromagnetic radiation 114). The photodetector 108 comprises a seconddoping type (e.g., n-type doping) opposite the first doping type. Insome embodiments, the first doping type is n-type and the second dopingtype is p-type, or vice versa. In further embodiments, the photodetector108 may be configured as and/or comprise a photodiode. An isolationstructure 106 is disposed within the substrate 104 and extends from thefront-side 104 f of the substrate 104 to a point above the front-side104 f. In some embodiments, the isolation structure 106 may comprise adielectric material (e.g., silicon dioxide, silicon nitride, siliconcarbide, etc.) and/or may be configured as a shallow trench isolation(STI) structure, deep trench isolation (DTI) structure, or anothersuitable isolation structure.

A back-side 104 b of the substrate 104 is disposed opposite thefront-side 104 f of the substrate 104. The back-side 104 b of thesubstrate 104 comprises a non-planar surface defining a plurality ofprotrusions 110 arranged in a periodic pattern. Thus, the protrusions110 may be or comprise a same material (e.g., silicon) as the substrate104. The plurality of protrusions 110 are laterally separated from oneanother by recesses within the back-side 104 b of the substrate 104. Theplurality of protrusions 110 each comprise opposing angled sidewalls.The protrusions 110 of the substrate 104 are configured, for example, toincrease a light receiving surface area for the incident electromagneticradiation 114 disposed upon the photodetector 108. This, in part,increases a sensitivity and/or a quantum efficiency (QE) of the imagesensor 100.

Further, a plurality of micro-lenses 112 are disposed within therecesses laterally between the protrusions 110, such that one of themicro-lenses 112 is disposed laterally between a corresponding pair ofprotrusions 110. In some embodiments, the micro-lenses 112 may, forexample, respectively be or comprise a dielectric material (e.g.,silicon dioxide) and/or may have a first index of refraction. It will beappreciated that other materials for the micro-lenses 112 are alsowithin the scope of the disclosure. In further embodiments, thesubstrate 104 comprises a semiconductor material (e.g., silicon)different than the dielectric material of the micro-lenses 112 and/orhas a second index of refraction different from the first index ofrefraction. It will be appreciated that other materials for thesubstrate 104 are also within the scope of the disclosure. In someembodiments, the second index of refraction is greater than the firstindex of refraction. In some embodiments, the micro-lenses 112respectively comprise a micro-lens protrusion 112 p that conforms tosidewalls of the protrusions 110 and fill the recesses between theprotrusions 110. In further embodiments, the micro-lenses 112 directlycontact the protrusions 110. Each of the micro-lenses 112 comprise aconvex upper surface 112 us that is curved and/or rounded outward in adirection away from the protrusions 110. As illustrated in FIG. 1, theincident electromagnetic radiation 114 (as illustrated by arrows) entersthe micro-lenses 112 through the convex upper surface 112 us. By virtueof the convex upper surface 112 us of each micro-lens 112, the incidentelectromagnetic radiation 114 is bent significantly and/or angledtowards a focal point 119 underlying the convex upper surface 112 us.The focal point 119 is disposed along a focal plane 120 that isvertically separated from a top surface 110 ts of the protrusions 110 bya first height h1 and that is vertically separated from a bottom surface110 bs of the protrusions by a second height h2. In some embodiments,the first height h1 is greater than the second height h2. In suchembodiments, this mitigates the incident electromagnetic radiation 114from reflecting off a sidewall of the protrusions 110 in a directionaway from the photodetector 108. In further embodiments, by virtue ofthe second height h2 being less than the first height hl, the angles ofincidence θ₁ of the incident electromagnetic radiation 114 upon asidewall of the protrusions 110 are significantly small, such that lightis not reflected away from the substrate 104. Other electromagneticradiation (not shown) that are not parallel to the incidentelectromagnetic radiation 114 and that enter the micro-lenses 112refract as described above and intersect other focal points along thefocal plane 120.

Further, after the incident electromagnetic radiation 114 is angledtowards the focal point 119 it may traverse sidewalls of the protrusions110. Since, in some embodiments, the micro-lenses 112 have the firstindex of refraction that is less than the second index of refraction ofthe underlying protrusions 110, the incident electromagnetic radiation114 will refract away from the corresponding normal axes 122 towards thephotodetector 108. In other words, the lower refractive index of themicro-lenses 112 relative to the protrusions 110 causes the incidentelectromagnetic radiation 114 to have an angle of refraction θ₂ that isless than a corresponding angle of incidence θ₁, thereby focusing theincident electromagnetic radiation 114 towards the photodetector 108.This increases absorption of the incident electromagnetic radiation 114by the substrate 104 (e.g., by reducing a reflection of the incidentelectromagnetic radiation 114 away from the protrusions 110). Increasingabsorption of the incident electromagnetic radiation 114 increases a QEof the photodetector 108, thereby increasing performance of the imagesensor 100.

FIG. 2 illustrates a cross-sectional view of some embodiments of animage sensor 200 corresponding to an alternative embodiment of the imagesensor 100 of FIG. 1.

In some embodiments, the image sensor 200 includes the substrate 104overlying the interconnect structure 102. The image sensor 200 may beconfigured as a back-side illuminated CMOS image sensor (BSI-CIS). Aplurality of semiconductor devices 212 are disposed within theinterconnect structure 102 and along the front-side 104 f of thesubstrate 104. In some embodiments, the semiconductor devices 212 may beconfigured as pixel devices that may output and/or process an electricalsignal generated by photodetectors 108. The semiconductor devices 212may, for example, be configured as transfer transistors, source-followertransistors, row select transistors, and/or reset transistors. It willbe appreciated that the semiconductor devices 212 being configured asother semiconductor devices is also within the scope of the disclosure.Further, the semiconductor devices 212 may each comprise a gatestructure 216 disposed along the front-side 104 f of the substrate 104,and a sidewall spacer structure 214 disposed along sidewalls of the gatestructure 216. In further embodiments, the gate structure 216 includes agate dielectric layer and a gate electrode, where the gate dielectriclayer is disposed between the substrate 104 and the gate electrode.

The interconnect structure 102 may include an interconnect dielectricstructure 206, a plurality of conductive wires 208, and a plurality ofconductive vias 210. In some embodiments, the interconnect dielectricstructure 206 comprises one or more inter-level dielectric (ILD) layersthat may respectively be or comprise an oxide, such as silicon dioxide,a fluorosilicate glass, a phosphate glass (e.g., borophosphate silicateglass), another suitable dielectric material, or any combination of theforegoing. It will be appreciated that the interconnect structure 206comprising other suitable materials is also within the scope of thedisclosure. The conductive wires and vias 208, 210 are disposed withinthe interconnect dielectric structure 206 and are configured toelectrically couple devices disposed within the image sensor 200 to oneanother and/or to another integrated chip (not shown). In someembodiments, the conductive wires and/or vias 208, 210 may, for example,respectively be or comprise copper, aluminum, titanium nitride, tantalumnitride, tungsten, another conductive material, or any combination ofthe foregoing. It will be appreciated that the conductive wires and/orvias 208, 210 comprising other suitable materials is also within thescope of the disclosure.

In some embodiments, the substrate 104 may be any semiconductor body(e.g., bulk silicon, another suitable semiconductor material, or thelike) and/or has a first doping type (e.g., p-type doping). Pixelregions 202 a-b are laterally separated from one another by a pluralityof isolation structures 106. In some embodiments, the plurality ofisolation structures 106 may be configured as STI structures, DTIstructures, back-side deep trench isolation (BDTI) structures, anothersuitable isolation structure, or any combination of the foregoing. Infurther embodiments, the isolation structures 106 may be or comprisesilicon dioxide, silicon nitride, silicon carbide, or the like. Further,a photodetector 108 is disposed within each of the pixel regions 202a-b. The photodetectors 108 may, for example, comprise a second dopingtype (e.g., n-type doping) that is opposite the first doping type. Itwill be appreciated that the photodetector 108 and/or the substrate 104comprising another doping type is also within the scope of thedisclosure.

In some embodiments, the photodetectors 108 may be configured togenerate electrical signals from near infrared (NIR) radiation thatincludes electromagnetic radiation within a first range of wavelengths.For example, the first range of wavelengths may be within a range ofabout 850 to 940 nanometers. It will be appreciated that other valuesfor the first range of wavelengths are also within the scope of thedisclosure. The substrate 104 has a thickness Ts that is defined betweenthe front-side 104 f of the substrate 104 and the back-side 104 b of thesubstrate 104. In some embodiments, the thickness Ts is within a rangeof about 4 to 6 micrometers. It will be appreciated that other valuesfor the thickness Ts are also within the scope of the disclosure. Thethickness Ts of the substrate 104 is selected to ensure high QE for thefirst range of wavelengths. For example, if the thickness Ts of thesubstrate 104 is thin (e.g., less than about 4 micrometers), then thephotodetectors 108 will have poor NIR light QE, which may decrease anability for phase detection. Further, if the thickness Ts of thesubstrate 104 is thick (e.g., greater than about 6 micrometers), thenplacement of pixel devices such as contact regions, isolationstructures, and/or transfer transistors may be adversely affectedwithout, for example, an increase of QE for NIR light.

The back-side 104 b of the substrate 104 comprises a plurality ofprotrusions 110 and a plurality of micro-lenses 112 are disposed betweenadjacent pairs of protrusions 110. The micro-lenses 112 each have aconvex upper surface 112 us configured to direct incident radiationtowards underlying photodetectors 108, as illustrated and described inFIG. 1. This increases a QE of the photodetectors 108, therebyincreasing a performance of the image sensor 200.

In further embodiments, the plurality of micro-lenses 112 may beconfigured as and/or referred to as a passivation layer thatcontinuously laterally extends across the back-side 104 b of thesubstrate 104. In such embodiments, the passivation layer overlies eachprotrusion 110 and comprises a plurality of upper convex protrusions 112up spaced laterally between adjacent pairs of the protrusions 110, andcomprises a plurality of lower protrusions 1121 p disposed below theupper convex protrusions 112 up. The lower protrusions 1121 p directlycontact sidewalls of the protrusions 110. Further, in some embodiments,the passivation layer may continuously laterally extend across theprotrusions 110 along an unbroken path.

FIG. 3A illustrates a cross-sectional view of some embodiments of animage sensor 300 a corresponding to an alternative embodiment of theimage sensor 200 of FIG. 2.

The image sensor 300 a includes an upper dielectric layer 302 overlyingthe micro-lenses 112 and the back-side 104 b of the substrate 104. Insome embodiments, the upper dielectric layer 302 may, for example, be orcomprise a plasma-enhanced oxide (PEOX) layer, silicon dioxide, oranother suitable dielectric material. It will be appreciated that othersuitable materials for the upper dielectric layer 302 are also withinthe scope of the disclosure. Further, a plurality of light filters 304(e.g., color filters, infrared (IR) filters, etc.) overlie the upperdielectric layer 302. The plurality of light filters 304 arerespectively configured to transmit specific wavelengths of incidentradiation. For example, a first light filter may transmit radiationhaving wavelengths within a first range, while a second light filter,adjacent to the first light filter, may transmit radiation havingwavelengths within a second range different than the first range. Inother embodiments, the light filters 304 may be configured as, forexample, color filters, where a first light filter is configured totransmit a first color (e.g., green light) and an adjacent second lightfilter is configured to transmits a second color (e.g., blue light)different than the first color. Further, a plurality of upper lenses 306are disposed over the plurality of light filters 304. Respective ones ofthe upper lenses 306 are laterally aligned with the light filters 304and overlie the pixel regions 202 a, 202 b. The plurality of upperlenses 306 are configured to focus incident electromagnetic radiationtowards the photodetectors 108, thereby further increasing the QE of thephotodetectors and a performance of the image sensor 300 a.

The photodetectors 108 are configured to generate electrical signalsfrom electromagnetic radiation with a wavelength λ. In some embodiments,the wavelength λ may include near infrared (NIR) radiation that includeselectromagnetic radiation within a range of about 850 to 940 nanometers.It will be appreciated that other values for the wavelength λ are alsowithin the scope of the disclosure. In other embodiments, a height hp ofthe protrusions 110 may be greater than about λ/2.5, thereby increasinga light receiving surface area for incident electromagnetic radiationdisposed upon the substrate 104. For example, the height hp may begreater than about 340 nanometers. It will be appreciated that othervalues for the height hp are also within the scope of the disclosure.This, in part, increases a sensitivity and/or QE of the image sensor 300a. A distance d1 is defined between top surfaces of two adjacentprotrusions 110. In further embodiments, the distance d1 may be greaterthan about λ/2, thereby increasing a light receiving surface area forincident electromagnetic radiation disposed upon the substrate 104. Forexample, the distance d1 may be greater than about 425 nanometers. Itwill be appreciated that other values for the distance d1 are alsowithin the scope of the disclosure. This, in part, further increases thesensitivity and/or QE of the image sensor 300 a. By virtue of the heighthp being greater than λ/2.5 and the distance d1 being greater than aboutλ/2, absorption of incident radiation with the wavelength λ by thesubstrate 104 is increased while decreasing reflection of the incidentradiation with the wavelength λ away from the photodetectors 108. Insome embodiments, the distance d1 is greater than the height hp.

FIG. 3B illustrates a cross-sectional view of some embodiments of animage sensor 300 b corresponding to some alternative embodiments of theimage sensor 300 a of FIG. 3A, where the upper dielectric layer 302 isomitted. In such embodiments, the plurality of light filters 304directly contact the plurality of micro-lenses 112.

FIGS. 4-9 illustrate cross-sectional views 400-900 of some embodimentsof a method of forming an image sensor that includes a substrate with aplurality of protrusions, and a plurality of micro-lenses disposed overand spaced between the protrusions according to the present disclosure.Although the cross-sectional views 400-900 shown in FIGS. 4-9 aredescribed with reference to a method, it will be appreciated that thestructures shown in FIGS. 4-9 are not limited to the method but rathermay stand alone separate of the method. Furthermore, although FIGS. 4-9are described as a series of acts, it will be appreciated that theseacts are not limiting in that the order of the acts can be altered inother embodiments, and the methods disclosed are also applicable toother structures. In other embodiments, some acts that are illustratedand/or described may be omitted in whole or in part.

As illustrated by the cross-sectional view 400 of FIG. 4, a substrate104 is provided and an isolation structure 106 is formed on a front-side104 f of the substrate 104. In some embodiments, the substrate 104 may,for example, be a bulk substrate (e.g., a bulk silicon substrate), asilicon-on-insulator (SOI) substrate, or another suitable substrate. Itwill be appreciated that other materials for the substrate 104 are alsowithin the scope of the disclosure. In some embodiments, before formingthe isolation structure 106, a first implant process is performed todope the substrate 104 with a first doping type (e.g., p-type). In someembodiments, a process for forming the isolation structure 106 mayinclude: selectively etching the substrate 104 to form a trench in thesubstrate 104 that extends into the substrate 104 from the front-side104 f of the substrate 104; and filling (e.g., by chemical vapordeposition (CVD), atomic layer deposition (ALD), physical vapordeposition (PVD), thermal oxidation, etc.) the trench with a dielectricmaterial (e.g., silicon nitride, silicon carbide, silicon dioxide,another suitable dielectric material, or any combination of theforegoing). In further embodiments, the substrate 104 is selectivelyetched by forming a masking layer (not shown) on the front-side 104 f ofthe substrate 104, and subsequently exposing the substrate 104 to one ormore etchants configured to selectively remove unmasked portions of thesubstrate 104.

Further, as shown in FIG. 4, a photodetector 108 is formed within thesubstrate 104. In some embodiments, the photodetector 108 includes aregion of the substrate 104 comprising a second doping type (e.g.,n-type) opposite the first doping type. In some embodiments, thephotodetector 108 may be formed by a selective ion implantation processthat utilizes a masking layer (not shown) on the front-side 104 f of thesubstrate 104 to selectively implant ions into the substrate. In furtherembodiments, the first doping type comprises p-type dopants and thesecond doping type comprises n-type dopants, or vice versa. Thephotodetector 108 is configured to generate electrical signals fromelectromagnetic radiation with a wavelength λ. In some embodiments, thewavelength λ may include near infrared (NIR) radiation that includeselectromagnetic radiation within a range of about 850 to 940 nanometers.It will be appreciated that other values for the wavelength λ are alsowithin the scope of the disclosure.

In addition, as illustrated in FIG. 4, after forming the photodetector108 a thinning process is performed on the back-side 104 b of thesubstrate 104 to reduce an initial thickness Ti of the substrate 104 toa thickness Ts. The thickness Ts is defined between the front-side 104 fof the substrate 104 and the back-side 104 b of the substrate 104. Insome embodiments, the thickness Ts is within a range of about 4 to 6micrometers. It will be appreciated that other values for the thicknessTs are also within the scope of the disclosure. In some embodiments, thethinning process may include performing a mechanical grinding process, achemical mechanical planarization (CMP) process, another suitablethinning process, or any combination of the foregoing.

As illustrated by the cross-sectional view 500 of FIG. 5, the structureof FIG. 4 is flipped and subsequently patterned to define a plurality ofprotrusions 110 along the back-side 104 b of the substrate 104. Theback-side 104 b of the substrate 104 is opposite the front-side 104 f ofthe substrate 104. In some embodiments, the plurality of protrusions 110are formed by performing one or more etch processes according to one ormore masking layers (not shown). The one or more etch processes may, forexample, include a wet etch process, a dry etch process, anothersuitable etch process, or any combination of the foregoing. Further, insome embodiments, the protrusions 110 are formed such that a height hpof the protrusions 110 may be greater than about λ/2.5, and a distanced1 may be greater than about λ/2, thereby increasing a light receivingsurface area for incident electromagnetic radiation disposed upon thesubstrate 104. The distance d1 is defined between top surfaces of twoadjacent protrusions 110. In yet further embodiments, the height hp maybe greater than about 340 nanometers and/or the distance d1 may begreater than about 425 nanometers. It will be appreciated that othervalues for the height hp and/or the distance d1 are also within thescope of the disclosure.

As illustrated by cross-sectional view 600 of FIG. 6, an upperdielectric layer 602 is deposited over the protrusions 110. An uppersurface of the upper dielectric layer 602 may correspond to the shape ofthe protrusions 110. In some embodiments, the upper dielectric layer 602may be deposited by, for example, CVD, ALD, PVD, thermal oxidation, aplasma enhanced deposition process (e.g., plasma-enhanced CVD (PECVD)),or another suitable deposition or growth process. Thus, the upperdielectric layer 602 may, for example, be or comprise a plasma enhancedoxide, silicon dioxide, silicon oxycarbide (SiOC), another suitabledielectric material, or any combination of the foregoing and/or may beformed to a thickness within a range of about 3,000 to 5,000 Angstroms.It will be appreciated that other values for the thickness of the upperdielectric layer 602 are also within the scope of the disclosure. In yetfurther embodiments, a bottom anti-reflective coating (BARC) layer 604is formed over the upper dielectric layer 602. In some embodiments, theBARC layer 604 may, for example, be formed by CVD, ALD, PVD, or anothersuitable deposition or growth process. In yet further embodiments, theBARC layer 604 may, for example, be or comprise a high-k dielectricmaterial (e.g., a dielectric material with a dielectric constant greaterthan 3.9), another suitable dielectric material, or any combination ofthe foregoing and/or may be formed to a thickness within a range ofabout 4,000 to 6,000 Angstroms. It will be appreciated that other valuesfor the thickness of the BARC layer 604 are also within the scope of thedisclosure. Thus, in some embodiments, the BARC layer 604 has a greaterthickness than the upper dielectric layer 602.

As illustrated by cross-sectional view 700 of FIG. 7, a first patterningprocess is performed on the BARC layer 604, thereby reducing an initialthickness of the BARC layer 604. In some embodiments, the firstpatterning process includes performing a dry etch process, a blanket dryetch process, or another suitable etch process. In further embodiments,the first patterning process may include exposing the BARC layer 604 toone or more etchants, such as oxygen (e.g., O₂), carbon monoxide (CO),another suitable etchant, or any combination of the foregoing. In yetfurther embodiments, the first patterning process does not etch theupper dielectric layer 602.

FIGS. 8A-8C illustrate cross-sectional views 800 a-c corresponding tosome embodiments of performing a second patterning process on the upperdielectric layer 602 and the BARC layer 604, thereby forming themicro-lenses 112. The second patterning process is performed in such amanner that the micro-lenses 112 each have a convex upper surface 112 usoverlying the protrusions 110. FIGS. 8A and 8B illustratecross-sectional views 800 a and 800 b corresponding to some embodimentsof a first snapshot and a second snapshot of the second patterningprocess. FIG. 8C illustrates a cross-sectional view 800 c correspondingto some embodiments of the micro-lenses 112 after completing the secondpatterning process.

In some embodiments, the second patterning process includes performing adry etch process, a blanket dry etch process, or another suitable etchprocess. In various embodiments, the second patterning process isperformed solely by a blanket dry etch process. In further embodiments,the second patterning process may include exposing the upper dielectriclayer 602 and the BARC layer 604 to one or more etchants, such aspolymer rich etchants, octafluorocyclobutane (e.g., C₄F₈),trifluoromethane (e.g., CHF₃), another suitable etchant, or anycombination of the foregoing. During the second patterning process, theupper dielectric layer 602 is etched at a first etch rate and the BARClayer 604 is etched at a second etch rate. In some embodiments, thefirst etch rate is at least 10 times greater than the second etch rate.In such embodiments, the second patterning process has a low selectivityfor the BARC layer 604 relative to the upper dielectric layer 602, suchthat the upper dielectric layer 602 is etched more quickly (e.g., atleast 10 times greater) than the BARC layer 604. This may be because theone or more etchants remove the upper dielectric layer 602 more quicklythan the BARC layer 604. By virtue of the first etch rate being at least10 times greater than the second etch rate, each of the micro-lenses 112have a convex upper surface 112 us. Thus, in some embodiments, a ratioof the first etch rate to the second etch rate is, for example, about10:1, about 11:1, about 12:1, within a range of about 10:1 to 20:1, orgreater than 10:1. It will be appreciated that other values for theratio of the first etch rate to the second etch rate are also within thescope of the disclosure. The convex upper surfaces 112 us of themicro-lenses 112 are each configured to bend and/or angle incidentelectromagnetic radiation towards a focal point underlying thecorresponding convex upper surface 112 us. This increases absorption ofthe incident electromagnetic radiation by the substrate 104 (e.g., byreducing a reflection of the incident electromagnetic radiation awayfrom the substrate 104). Increasing absorption of the incidentelectromagnetic radiation increases a QE of the photodetector 108.

The cross-sectional view 800 a of FIG. 8A illustrates some embodimentsof a first snapshot of the second patterning process taken at a firsttime, where the upper dielectric layer 602 is removed more quickly thanthe BARC layer 604. Further, the cross-sectional view 800 b of FIG. 8Billustrates some embodiments of a second snapshot of the secondpatterning process taken at a second time, where the second snapshot istaken at some time after the first snapshot. As illustrated by the FIG.8B, remnants of BARC layer 604 are disposed along the top surface of theupper dielectric layer 602, such that an upper surface of the BARC layer604 and the upper dielectric layer 602 laterally spaced between adjacentpairs of the protrusions 110 is curved and/or rounded outward in adirection away from the protrusions 110 (i.e., convex). Thecross-sectional view 800 c of FIG. 8C illustrates some embodiments ofthe micro-lenses 112 after performing the second patterning process onthe upper dielectric layer 602 and the BARC layer 604. The convex uppersurface 112 us of each of the micro-lenses 112 corresponds to the curvedupper surface of the BARC layer 604 and the upper dielectric layer 602illustrated in FIG. 8B.

As illustrated by cross-sectional view 900 of FIG. 9, a light filter 304is formed over the micro-lenses 112. The light filter 304 is formed ofmaterial that allows for the transmission of incident electromagneticradiation (e.g., light) having a specific wavelength range, whileblocking incident wavelength with another wavelength outside of thespecified range. In further embodiments, the light filter 304 may beformed by CVD, PVD, ALD, sputtering, or the like and/or may beplanarized (e.g., via a chemical mechanical planarization (CMP) process)subsequent to formation. Further, an upper lens 306 is formed over thelight filter 304. In some embodiments, the upper lens 306 may be formedby depositing (e.g., by CVD, PVD, etc.) a lens material on the lightfilter 304. A lens template (not shown) having a curved upper surface ispatterned above the lens material. The upper lens 306 is then formed byselectively etching the lens material according to the lens template.

FIG. 10 illustrates a method 1000 of forming an image sensor thatincludes a substrate with a plurality of protrusions, and a plurality ofmicro-lenses disposed over and spaced between the protrusions inaccordance with some embodiments of the present disclosure. Although themethod 1000 is illustrated and/or described as a series of acts orevents, it will be appreciated that the method is not limited to theillustrated ordering or acts. Thus, in some embodiments, the acts may becarried out in different orders than illustrated, and/or may be carriedout concurrently. Further, in some embodiments, the illustrated acts orevents may be subdivided into multiple acts or events, which may becarried out at separate times or concurrently with other acts orsub-acts. In some embodiments, some illustrated acts or events may beomitted, and other un-illustrated acts or events may be included.

At act 1002, an isolation structure is formed in a front-side of asubstrate. FIG. 4 illustrates a cross-sectional view 400 correspondingto some embodiments of act 1002.

At act 1004, a photodetector is formed within the substrate. FIG. 4illustrates a cross-sectional view 400 corresponding to some embodimentsof act 1004.

At act 1006, a plurality of protrusions are formed in a back-side of thesubstrate. The protrusions overlie the photodetector. FIG. 5 illustratesa cross-sectional view 500 corresponding to some embodiments of act1006.

At act 1008, an upper dielectric layer is deposited over the pluralityof protrusions. Further, a bottom anti-reflective coating (BARC) layeris deposited over the upper dielectric layer. FIG. 6 illustrates across-sectional view 600 corresponding to some embodiments of act 1008.

At act 1010, a first patterning process is performed on the BARC layer.FIG. 7 illustrates a cross-sectional view 700 corresponding to someembodiments of act 1010.

At act 1012, a second patterning process is performed on the upperdielectric layer and the BARC layer. The upper dielectric layer isetched more quickly than the BARC layer. Further, the second patterningprocess defines a plurality of micro-lenses over the protrusions suchthat each micro-lens has a convex upper surface. FIGS. 8A-8C illustratecross-sectional views 800 a-c corresponding to some embodiments of act1012.

At act 1014, a light filter is formed over the plurality ofmicro-lenses. FIG. 9 illustrates a cross-sectional view 900corresponding to some embodiments of act 1014.

At act 1016, an upper lens is formed over the light filter. FIG. 9illustrates a cross-sectional view 900 corresponding to some embodimentsof act 1014.

Accordingly, in some embodiments, the present disclosure relates to animage sensor including a substrate with a plurality of protrusionsdisposed along a back-side of the substrate. Further, a plurality ofmicro-lenses are disposed over and spaced laterally between theprotrusions. The micro-lenses each comprise a convex upper surfaceconfigured to direct incident radiation to a focal point underlying theconvex upper surface.

In some embodiments, the present application provides an image sensor,including: a substrate including a plurality of sidewalls that define aplurality of protrusions along a first side of the substrate, whereinthe substrate has a first index of refraction; a photodetector disposedwithin the substrate and underlying the plurality of protrusions; and aplurality of micro-lenses overlying the first side of the substrate,wherein the micro-lenses have a second index of refraction that is lessthan the first index of refraction, wherein the micro-lenses arerespectively disposed laterally between and directly contact an adjacentpair of protrusions in the plurality of protrusions, and wherein themicro-lenses respectively comprise a convex upper surface.

In some embodiments, the present application provides an integratedchip, including: a substrate including a plurality of first protrusionsalong a back-side of the substrate, where the substrate comprises afirst material with a first index of refraction; an interconnectstructure disposed along a front-side of the substrate; a photodetectordisposed within the substrate and underlying the plurality of firstprotrusions; a passivation layer arranged on and between the pluralityof first protrusions, wherein the passivation layer includes a pluralityof second protrusions along an upper surface of the passivation layer,wherein the plurality of second protrusions is different than theplurality of first protrusions, wherein the passivation layer comprisesa second material with a second index of refraction different from thefirst index of refraction; and a light filter overlying the passivationlayer.

In some embodiments, the present application provides a method forforming an image sensor, the method includes performing an ion implantprocess to define a photodetector within a substrate; etching a firstside of the substrate to define a plurality of protrusions overlying thephotodetector; depositing a dielectric layer over the plurality ofprotrusions, wherein the dielectric layer comprises a first material;depositing an anti-reflection coating (ARC) layer over the dielectriclayer, wherein the ARC layer comprises a second material different thanthe first material; performing a first patterning process on the ARClayer; and performing a second patterning process on the dielectriclayer and the ARC layer, thereby defining a plurality of micro-lensesthat respectively have a concave upper surface, wherein the dielectriclayer is etched at a first rate during the second patterning process andthe ARC layer is etched at a second rate during the second patterningprocess, wherein the first rate is greater than the second rate.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An image sensor, comprising: a substratecomprising a plurality of sidewalls that define a plurality ofprotrusions along a first side of the substrate, wherein the substratehas a first index of refraction; a photodetector disposed within thesubstrate and underlying the plurality of protrusions; and a pluralityof micro-lenses overlying the first side of the substrate, wherein themicro-lenses have a second index of refraction that is less than thefirst index of refraction, wherein the micro-lenses are respectivelydisposed laterally between and directly contact an adjacent pair ofprotrusions in the plurality of protrusions, and wherein themicro-lenses respectively comprise a convex upper surface.
 2. The imagesensor of claim 1, wherein the plurality of protrusions are laterallyseparated from one another by recesses within the first side of thesubstrate, wherein the plurality of micro-lenses respectively comprise alens protrusion that fills a corresponding recess.
 3. The image sensorof claim 1, wherein the substrate comprises silicon and the micro-lensescomprise silicon dioxide.
 4. The image sensor of claim 1, wherein aheight of the plurality of micro-lenses is greater than a height of theprotrusions.
 5. The image sensor of claim 1, wherein the plurality ofprotrusions comprise a first protrusion and a second protrusion disposedlaterally adjacent to one another, wherein the first protrusioncomprises a first top point and the second protrusion comprises a secondtop point, wherein a height of the plurality of protrusions is less thana lateral distance between the first top point and the second top point.6. The image sensor of claim 5, wherein the plurality of micro-lensescomprises a first micro-lens disposed between the first and secondprotrusions, wherein a convex upper surface of the first micro-lens isspaced laterally between the first top point of the first protrusion andthe second top point of the second protrusion.
 7. The image sensor ofclaim 6, wherein the first micro-lens is configured to direct incidentelectromagnetic radiation towards a focal point underlying the convexupper surface of the first micro-lens, wherein the focal point is spacedlaterally between the first and second protrusions, and wherein thefocal point is spaced vertically above a bottom surface of the pluralityof protrusions.
 8. An integrated chip, comprising: a substratecomprising a plurality of first protrusions along a back-side of thesubstrate, where the substrate comprises a first material with a firstindex of refraction; an interconnect structure disposed along afront-side of the substrate; a photodetector disposed within thesubstrate and underlying the plurality of first protrusions; apassivation layer arranged on and between the plurality of firstprotrusions, wherein the passivation layer comprises a plurality ofsecond protrusions along an upper surface of the passivation layer,wherein the plurality of second protrusions is different than theplurality of first protrusions, wherein the passivation layer comprisesa second material with a second index of refraction different from thefirst index of refraction; and a light filter overlying the passivationlayer.
 9. The integrated chip of claim 8, wherein the first protrusionsrespectively have a triangular shape and the second protrusionsrespectively have a semicircular shape.
 10. The integrated chip of claim8, wherein a lower surface of the passivation layer comprises aplurality of third protrusions that engagedly meet a plurality ofrecesses spaced between the plurality of first protrusions of thesubstrate.
 11. The integrated chip of claim 8, wherein the first indexof refraction is at least two times greater than the second index ofrefraction.
 12. The integrated chip of claim 8, wherein thephotodetector is configured to generate electrical signals from nearinfrared (NIR) radiation.
 13. The integrated chip of claim 12, wherein athickness of the substrate is within a range of about 4 to 6micrometers.
 14. The integrated chip of claim 8, further comprising: anupper lens overlying the light filter, wherein an upper surface of theupper lens is convex.
 15. The integrated chip of claim 8, wherein abottom surface of the light filter directly contacts the plurality ofsecond protrusions.
 16. A method of forming an image sensor, comprising:performing an ion implant process to define a photodetector within asubstrate; etching a first side of the substrate to define a pluralityof protrusions overlying the photodetector; depositing a dielectriclayer over the plurality of protrusions, wherein the dielectric layercomprises a first material; depositing an anti-reflection coating (ARC)layer over the dielectric layer, wherein the ARC layer comprises asecond material different than the first material; performing a firstpatterning process on the ARC layer; and performing a second patterningprocess on the dielectric layer and the ARC layer, thereby defining aplurality of micro-lenses that respectively have a concave uppersurface, wherein the dielectric layer is etched at a first rate duringthe second patterning process and the ARC layer is etched at a secondrate during the second patterning process, wherein the first rate isgreater than the second rate.
 17. The method of claim 16, wherein thesecond patterning process includes performing a blanket dry etchprocess.
 18. The method of claim 16, further comprising: forming a lightfilter over the plurality of micro-lenses such that the light filterdirectly contacts the micro-lenses.
 19. The method of claim 18, furthercomprising: forming an upper lens over the light filter such that theupper lens has a curved upper surface.
 20. The method of claim 16,wherein the second patterning process includes exposing the dielectriclayer and the ARC layer to one or more etchants, wherein the one or moreetchants comprise octafluorocyclobutane and/or trifluoromethane.